Occurrence
This disease is observed between late
spring and the summer seasons, especially
during periods of frequent rainfall. Areas of
St. Augustinegrass that are under cultural or
environmental stresses are more susceptible to
disease development. Areas of turf under low
fertility or sub-optimal light conditions seem
to develop this disease.

Symptoms/Signs
Initial symptoms are narrow, dark
brown leaf spots that enlarge over time into
oblong to irregularly shaped lesions with dark
tan centers and dark brown to purple margins
(Figure 1). Under humid conditions, the abun-
dant sporulation of the pathogen in the lesion
centers may confer a whitish sheen to the spots.

Numerous spots on multiple leaves can
cause extensive yellowing and withering of the
canopy. This disease is very similar in pattern
on the lawn and symptoms to that of gray leaf
spot, but management is very different.

Cultural Controls

Prevent the disease by fertilizing ad-

equately, using slow-release nitrogen sources
balanced with potassium, preferably a slow-
release potassium form. Examine the irrigation
cycle for timing, frequency and amount. Time
irrigation so as not to extend the dew period
(between 2 and 8 AM). Water only when the
turf exhibits moisture stress. Avoid daily, fre-
quent irrigation cycles that promote foliar dis-
ease.
If Cercospora leaf spot is already
present, the disease can be managed with the
application of quick release nitrogen in a fertil-
izer blend balanced with potassium (N:K ratio
of 1:1). Apply 12 pound N per 1000 square feet
utilizing an ammonium nitrate, ammonium
sulfate or quick release urea formulation.

Where this disease is persistent, choice
of St. Augustinegrass cultivars derived from
'bitter blue' types offer more resistance to this
disease.
Chemical Controls

Mancozeb can be applied to a residential
lawn only by a professional pesticide applica-
tor. Chlorothalonil cannot be applied to a
residential lawn, but it can be applied to
turfgrass in a business or industrial land-
scape.
Referto "Turfgrass Disease Management" PPP-
64 for explanations of chemical and cultural
controls.